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Jl ( 

An Inquiry into 

The Psychic Powers of these Animals 

With an Appendix on 

The Peculiarities of Their Olfactory Sense 


Dr. August For el 

Late Professor of Psychiatry at the University of Zurich 

Translated from the German 

Prof. William Morton Wheeler 

American Museum of Natural History, New York 

The Open Court Publishing Company 

Kegan Paul, Trench, Trubner &* Co. Ltd. 





WHEN discussing the ant-mind, we must consider that these 
small animals, on the one hand, differ very widely from our- 
selves in organisation, but on the other hand, have come, through 
so-called convergence, to possess in the form of a social common- 
wealth a peculiar relationship to us. My subject, however, requires 
the discussion of so many complicated questions that I am com- 
pelled to assume acquaintance with the work of others, especially 
the elements of psychology, and in addition the works of P. Huber, 
Wasmann, von Buttel-Reepen, Darwin, Romanes, Lubbock, my 
Fourmis de la Sutsse, and many others. Since the functions ot the 
sense-organs constitute the basis of comparative psychology, I 
must also refer to a series of articles entitled "Sensations des In- 
sectes" which I have recently published (1900-1901) in the Rivista 
de Biologia Generate, edited by Dr. P. Celesia. In these papers I 
have defined my position with respect to various authors, especially 
Plateau and Bethe. 

Very recently Bethe, Uexkull, and others have denied the ex- 
istence of psychic powers in invertebrate animals. They explain 
the latter as reflex-machines, and take their stand on the ground of 
the so-called psycho-physical parallelism for the purpose of demon- 
strating our inability to recognise mental qualities in these animals. 
They believe, however, that they can prove the mechanical regu- 
larity of behavior, but assume unknown forces whenever they are 
left in the lurch in their explanations. They regard the mind as 
first making its appearance in the vertebrates, whereas the old Car- 
tesians regarded all animals, in contradistinction to man, as mind- 
less (unconscious) machines. 


v v^ 

The Jesuit father E. Wasmann and von Buttel-Reepen are 
willing, on the other hand, to accept the inductive inference from 

analogy as a valid scientific method. Like Lubbock, the lecturer 
\ v 

. and others, they advocate a comparative psychology of the inverte- 
brates and convincingly demonstrate the existence of psychic facul- 
ties in these animals. Wasmann, however, puts a very low esti- 
mate on the mental powers of the higher vertebrates and, in my 
opinion, improperly, denies to them any ability of drawing infer- 
ences from experience when in the presence of new conditions (this 
alone he designates as intelligence); he believes that man alone 
possesses an immortal soul (independent of natural laws?) in addi- 
tion to the animal mind. 

It is necessary, first of all, to arrive at some common under- 
standing concerning the obscure notion "psychic" in order that 
we may avoid logomachy, and carrying on theology in the sense of 
Goethe's Mephistopheles. Two concepts are confounded in an 
obscure manner in the word "psychic" : first, the abstract concept 
of introspection, or subjectivism, i. e. , observation from within, 
which every person knows only, and can know only, in and by him- 
self. For this let us reserve the term "consciousness." Second, 
the "activity" of the mind or that which determines the contents 
of the field of consciousness. This has been included without fur- 
ther ado with consciousness in the wider sense, and thence has 
arisen the confusion of regarding consciousness as an attribute of 
the mind. In another place I have designated the molecular wave 
of activity of the neural elements as "neurocyme." 

We cannot speak of the consciousness of human beings other 
than ourselves without drawing an inference from analogy ; quite 
as little ought we to speak of a consciousness of forgotten things. 
The field of our consciousness is constantly changing. Things ap- 
pear in it and disappear from it. Memory, through association, 
enables us to recall, more or less directly and with more or less diffi- 
culty, things which appear to be momentarily absent from con- 
sciousness. Moreover, both the experience of self-observation and 
the phenomena of hypnotism teach us experimentally that many 
things of which we seem to be unconscious, are nevertheless pres- 


ent in consciousness or have been. Indeed, certain sense-impres- 
sions remain, at the moment of their occurrence, unconscious so 
far as our ordinary consciousness or superconsciousness is con- 
cerned, although they can be subsequently recalled into conscious- 
ness by suggestion. Whole chains of brain-activities, (dreams, 
somnambulism, or secondary consciousness) seem ordinarily to be 
excluded from the superconsciousness, but may subsequently be 
associated by suggestion with the remembered contents of con- 
sciousness. In all these cases, therefore, what seems to be uncon- 
scious is after all proved to be conscious. The above-mentioned 
phenomena have frequently led to mystical interpretations, but 
they are explainable on a very simple assumption. Let us assume 
and this is quite in harmony with observation that the fields of 
the introspectively conscious brain-activities are limited by so-called 
association or dissociation processes, i. e., that we are unable ac- 
tively to bring them all into connection at the same time, and that 
therefore all that seems to us unconscious has also in reality a con- 
sciousness, in other words, a subjective reflex, then the following 
results : Our ordinary waking consciousness or superconsciousness 
is merely an inner subjective reflex of those activities of attention 
which are most intimately connected with one another, i. e., of the 
more intensively concentrated maxima of our cerebral activities 
during waking. There exist, however, other consciousnesses, partly 
forgotten, partly only loosely or indirectly connected with the con- 
tents of the superconsciousness, in contradistinction to which these 
may be designated as subconsciousness. They correspond to other 
less concentrated or otherwise associated cerebral activities. We 
are bound to assume the existence of still more remotely intercon- 
nected subconsciousnesses for the infra-cortical (lower) brain- 
centers, and so on. 

It is easy to establish the fact that the maximum of our psychic 
activity, namely, attention, passes every moment from one percep- 
tion or thought to another. These objects of attention, as visual 
or auditory images, will-impulses, feelings or abstract thoughts, 
come into play and of this there is no doubt in different brain- 
regions or neuron-complexes. We can therefore compare attention 


to a functional macula lutea wandering in the brain, or with a wan- 
dering maximal intensity of neurocymic activity. But it is quite as 
satisfactorily established that other psychic phenomena external to 
attention are likewise present in consciousness, though in a feebler 
condition. Finally, it is well known that all that has been in con- 
sciousness even that which is now more, now less, forgotten is 
included in the psychic, i. e., in the contents of consciousness. On 
superficial consideration this appears to satisfy theoretical require- 
ments. But in fact and in truth there are innumerable processes 
of which we are feebly conscious for only a scarcely appreciable 
instant and which anon disappear from consciousness. Here and 
not in the strong and repeated "psychomes" I beg your indul- 
gence for this word, with which I would for the sake of brevity 
designate each and every psychic unit are we to seek the transi- 
tion from the conscious to the apparently unconscious. Even in 
this case, however, the feeble condition of consciousness is only 
apparent, because the inner reflex of these processes can merely 
echo faintly in the field of a strongly diverted attention. This, 
therefore, in no wise proves that such half conscious processes are 
in and for themselves so feebly represented in consciousness, since 
a flash of attention is sufficient subsequently to give them definite 
shape in consciousness. Only in consequence of the diversion of 
the attention do they lose more and more their connection with the 
chain of intensity-maxima which, under ordinary circumstances, 
constitute the remembered contents of our superconsciousness. 
The more feebly, however, they are bound to the latter, with the 
more difficulty are such half-conscious processes later associated 
anew through memory with the dominant chain. Of such a nature 
are all dreams, all the subordinate circumstances of our lives, all 
automatised habits, all instincts. But if there exists between the 
clearly conscious and the unconscious, a half-conscious brain-life, 
whose consciousness appears to us so feeble merely on account of 
the deviation of our ordinary train of memories, this is an unequiv- 
ocal indication that a step further on the remaining connection 
would be completely severed, so that we should no longer have the 
right to say that the brain-activities thus fading away nebulously 


from our superconsciousness do not have consciousness in and for 
themselves. For the sake of brevity and simplicity we will ascribe 
subconsciousness to these so-called unconscious brain -processes. 

If this assumption is correct and all things point in this di- 
rection we are not further concerned with consciousness. It does 
not at all exist as such, but only through the brain-activity of which 
it is the inner reflex. With the disappearance of this activity, con- 
sciousness disappears. When the one is complicated, the other, 
too, is complicated. When the one is simple, the other is corre- 
spondingly simple. If the brain-activity be dissociated, conscious- 
ness also becomes dissociated. Consciousness is only an abstract 
concept, which loses all its substance with the falling away of 
"conscious" brain-activity. The brain-activity reflected in the 
mirror of consciousness appears therein subjectively as a summary 
synthesis, and the synthetical summation grows with the higher 
complications and abstractions acquired through habit and prac- 
tice, so that details previously conscious (e. g., those involved in 
the act of reading) later become subconscious, and the whole takes 
on the semblance of a psychical unit. 

Psychology, therefore, cannot restrict itself merely to a study 
of the phenomena of our superconsciousness by means of intro- 
spection, for the science would be impossible under such circum- 
stances. Everybody would have only his own subjective psychol- 
ogy, after the manner of the old scholastic spiritualists, and would 
therefore be compelled to doubt the very existence of the external 
world and his fellow-men. Inference from analogy, scientific in- 
duction, the comparison of the experiences of our five senses, prove 
to us the existence of the outer world, our fellow-men and the psy- 
chology of the latter. They also prove to us that there is such a 
thing as comparative psychology, a psychology of animals. Finally 
our own psychology, without reference to our brain--activity, is an 
incomprehensible patchwork full of contradictions, a patchwork 
which above all things seems to contradict the law of the conser- 
vation of energy. 

It follows, furthermore, from these really very simple reflections 
that a psychology that would ignore brain-activity, is a monstrous 


impossibility. The contents of our superconsciousness are con- 
tinually influenced and conditioned by subconscious brain-activi- 
ties. Without these latter it can never be understood. On the 
other hand, we understand the full value and the ground of the 
complex organisation of our brain only when we observe it in the 
inner light of consciousness, and when this observation is supple- 
mented by a comparison of the consciousness of our fellow-men as 
this is rendered possible for us through spoken and written lan- 
guage by means of very detailed inferences from analogy. The 
mind must therefore be studied simultaneously from within and 
from without. Outside ourselves the mind can, to be sure, be 
studied only through analogy, but we are compelled to make use of 
this the only method which we possess. 

Some one has said that language was given to man not so 
much for the expression as for the concealment of his thoughts. It 
is also well known that different men in all honesty attribute very 
different meanings to the same words. A savant, an artist, a 
peasant, a woman, a wild Wedda from Ceylon, interpret the same 
words very differently. Even the same individual interprets them 
differently according to his moods and their context. Hence it 
follows that to the psychologist and especially to the psychiatrist 
and as such I am here speaking the mimetic expression, glances 
and acts of a man often betray his true inner being better than his 
spoken language. Hence also the attitudes and behavior of ani- 
mals have for us the value of a "language," the psychological im- 
portance of which must not be underestimated. Moreover, the 
anatomy, physiology and pathology of the animal and human brain 
have yielded irrefutable proof that our mental faculties depend on 
the quality, quantity, and integrity of the living brain and are one 
with the same. It is just as impossible that there should exist a 
human brain without a mind, as a mind without a brain, and to 
every normal or pathological change in the mental activity, there 
corresponds a normal or pathological change of the neurocymic ac- 
tivity of the brain, i. e., of its nervous elements. Hence what we 
perceive introspectively in consciousness is cerebral activity. 

As regards the relation of pure psychology (introspection") to 


the physiology of the brain (observation of brain-activity from with- 
out), we shall take the theory of identity for granted so long as it 
is in harmony with the facts. The word identity, or monism, im- 
plies that every psychic phenomenon is the same real thing as the 
molecular or neurocymic activity of the brain-cortex coinciding 
with it, but that this may be viewed from two standpoints. The 
phenomenon alone is dualistic, the thing itself is monistic. If this 
were otherwise there would result from the accession of the purely 
psychical to the physical, or cerebral, an excess of energy which 
would necessarily contradict the law of the conservation of energy. 
Such a contradiction, however, has never been demonstrated and 
would hold up to derision all scientific experience. In the mani- 
festations of our brain-life, wonderful as they undoubtedly are, 
there is absolutely nothing which contradicts natural laws and jus- 
tifies us in postulating the existence of a mythical, supernatural 

On this account I speak of monistic identity and not of psycho- 
physical parallelism. A thing cannot be parallel with itself. Of 
course, psychologists of the modern school, when they make use of 
this term, desire merely to designate a supposed parallelism of 
phenomena without prejudice either to monism or dualism. Since, 
however, many central nervous processes are accessible neither to 
physiological nor to psychological observation, the phenomena ac- 
cessible to us through these two methods of investigation are not 
in the least parallel, but separated from one another. very unequally 
by intermediate processes. Moreover, inasmuch as the dualistic 
hypothesis is scientifically untenable, it is altogether proper to 
start out from the hypothesis of identity. 

It is as clear as day that the same activity in the nervous sys- 
tem of an animal, or even in my own nervous system, observed by 
myself, first by means of physiological methods from without, and 
second, as reflecting itself in my consciousness, must appear to me 
to be totally different, and it would indeed be labor lost to try to 
convert the physiological into psychological qualities or vice versa. 
We cannot even convert one psychological quality into another, so 
far as the reality symbolised by both is concerned ; e. g., the tone, 


the visual and tactile sensation, which a uniform, low, tuning-fork 
vibration produces on our three corresponding senses. Neverthe- 
less, we may infer inductively that it is the same reality, the same 
vibration which is symbolised for us in these three qualitatively 
and totally different modes; i. e., produces in us these three differ- 
ent psychical impressions which cannot be transformed into one 
another. These impressions depend on activities in different parts 
of the brain and are, of course, as such actually different from one 
another in the brain. We speak of psycho-physiological identity 
only when we mean, on the one hand, the cortical neurocyme which 
directly conditions the-tonscious phenomena known to us, on the 
other hand, the corresponding phenomena of consciousness. 

And, in fact, a mind conceived as dualistic could only be de- 
void of energy or energy-containing. If it be conceived as devoid 
of energy (Wasmann), i. e., independent of the laws of energy, 
we have arrived at a belief in the miraculous, a belief which coun- 
tenances the interference with and arbitrary suspension of the laws 
of nature. If it be conceived as energy-containing, one is merely 
playing upon words, for a mind which obeys the law of energy is 
only a portion of the cerebral activities arbitrarily severed from its 
connections and dubbed "psychic essence," only that this maybe 
forthwith discredited. Energy can only be transformed qualita- 
tively, not quantitatively. A mind conceived as dualistic, if sup- 
posed to obey the law of energy, would have to be transformed 
completely into some other form of energy. But then it would no 
longer be dualistic, i. e., no longer essentially different from the 

Bethe, Uexkull, and others would require us to hold fast to 
the physiological method, because it alone is exact and restricts it- 
self to what can be weighed and measured. This, too, is an error 
which has been refuted from time immemorial. Only pure mathe- 
matics is exact, because in its operations it makes use solely of 
equations of abstract numbers. The concrete natural sciences can 
never be exact and are as unable to subsist without the inductive 
method of inference from analogy as a tree without its roots. Bethe 
and Uexkull do not seem to know that knowledge is merely rela- 


tive. They demand absolute exactitude and cannot understand 
that such a thing is impossible. Besides, physiology has no reason 
to pride itself upon the peculiar exactitude of its methods and re- 

Although we know that our whole psychology appears as the 
activity of our cerebrum in connection with the activities of more 
subordinate nerve-centers, the senses and the muscles, nevertheless 
for didactic purposes it may be divided into the psychology of cog- 
nition, of feeling and Volition. Relatively speaking, this subdivi- 
sion has an anatomico-physiological basis. Cognition depends, in 
the first instance, on the elaboration of sen^e- impressions by the 
brain ; the will represents the psycho- or-eerebrofugal resultants of 
cognition and the feelings together with their final transmission to 
the musclers. The feelings represent general conditions of excita- 
tion of a central nature united with elements of cognition and with 
cerebrofugal impulses, which are relatively differentiated and re- 
fined by the former, but have profound hereditary and phylogenetic 
origins and are relatively independent. There is a continual inter- 
action of these three groups of brain-activities upon one another. 
Sense-impressions arouse the attention ; this necessitates move- 
ments ; the latter produce new sense-impressions and call for an 
active selection among themselves. Both occasion feelings of pleas- 
ure and pain and these again call forth movements of defense, 
flight, or desire, and bring about fresh sense-impressions, etc. 
Anatomically, at least, the sensory pathways to the brain and their 
cortical centers are sharply separated from the centers belonging 
to the volitional pathways to the muscles. Further on in the cere- 
brum, however, all three regions merge together in many neurons 
of the cortex. 

Within ourselves, moreover, we are able to observe in the three 
above-mentioned regions all varieties and degrees of so-called 
psychic dignity, from the simplest reflex to the highest mental 
manifestations. The feelings and impulses connected with self- 
preservation (hunger, thirst, fear) and with reproduction (sexual 
love and its concomitants) represent within us the region of long- 
inherited, profoundly phyletic, fixed, instinct-life. These instincts 


are nevertheless partially modified and partly kept within due 
bounds through the interference of the higher cerebral activities. 
The enormous mass of brain-substance, which in man stands in no 
direct relation to the senses and musculature, admits not only of 
an enormous storing up of impressions and of an infinite variety of 
motor innervations, but above all, of prodigious combinations of 
these energies among themselves through their reciprocal activities 
and the awakening of old, so-called memory images through the 
agency of new impressions. In contradistinction to the compul- 
sory, regular activities of the profoundly phyletic automatisms, I 
have used the term "plastic" to designate those combinations and 
individual adaptations which depend on actual interaction in the 
activities of the cerebrum. Its loftiest and finest expression is the 
plastic imagination, both in the province of cognition and in the 
province of feeling, or in both combined. In the province of the 
will the finest plastic adaptability, wedded to perseverance and 
firmness, and especially when united with the imagination, yields 
that loftiest mental condition which gradually brings to a conclu- 
sion during the course of many years decisions that have been long 
and carefully planned and deeply contemplated. Hence the plas- 
tic gift of combination peculiar to genius ranks much higher than 
any simpler plastic adaptability. 

The distinction between automatism and plasticity in brain- 
activity is, however, only a relative one and one of degree. In the 
most different instincts which we are able to influence through our 
cerebrum, i. e., more or less voluntarily, like deglutition, respira- 
tion, eating, drinking, the sexual impulse, maternal affection, jeal- 
ousy, we observe gradations between compulsory heredity and plas- 
tic adaptability, yes, even great individual fluctuations according 
to the intensity of the corresponding hereditary predispositions. 

Now it is indisputable that the individual Pithecanthropus or 
allied being, whose cerebrum was large enough gradually to con- 
struct from onomatopceas, interjections and the like, the elements 
of articulate speech, must thereby have acquired a potent means of 
exploiting his brain. Man first fully acquired this power through 
written language. Both developed the abstract concept symbolised 


by words, as a higher stage in generalisation. All these things 
give man a colossal advantage, since he is thereby enabled to stand 
on the shoulders of the written encyclopaedia of his predecessors. 
This is lacking in all animals living at the present time. Hence, if 
we would compare the human mind with the animal mind, we must 
turn, not to the poet or the savant, but to the Wedda or at any rate 
to the illiterate. These people, like children and animals, are very 
simple and extremely concrete in their thinking. The fact that it 
is impossible to teach a chimpanzee brain the symbols of language 
proves only that it is not sufficiently developed for this purpose. 
But the rudiments are present nevertheless. Of course the "lan- 
guage" of parrots is no language, since it symbolises nothing. On 
the other hand, some animals possess phyletic, i. e., hereditarily 
and instinctively fixed cries and gesture, which are as instinctively 
understood. Such instinctive animal languages are also very widely 
distributed and highly developed among insects, and have been 
fixed by heredity for each species. Finally it is possible to develop 
by training in higher animals a certain mimetic and acoustic conven- 
tional language-symbolism, by utilising for this purpose the pecu- 
liar dispositions of such species. Thus it is possible to teach a 
dog to react in a particular manner to certain sounds or signs, but 
it is impossible to teach a fish or an ant these things. The dog 
comprehends the sign, not, of course, with the reflections of human 
understanding, but with the capacity of a dog's brain. And it is, 
to be sure, even more impossible to teach its young an accomplish- 
ment so lofty for its own brain as one which had to be acquired by 
training, than for the Wedda or even the negro to transmit his ac- 
quired culture by his own impulse. Even the impulse to do this is 
entirely lacking. Nevertheless, every brain that is trained by man 
is capable of learning and profiting much from the experience of 
its own individual life. And one discovers on closer examination 
that even lower animals may become accustomed to some extent to 
one thing or another, and hence trained, although this does not 
amount to an understanding of conventional symbols. 

In general we may say, therefore, that the central nervous sys- 
tem operates in two ways : automatically and plastically. 


The so-called reflexes and their temporary, purposefully adap- 
tive, but hereditarily stereotyped combinations, which respond 
always more or less in the same manner to the same stimuli, con- 
stitute the paradigm of automatic activities. These have the de- 
ceptive appearance of a "machine" owing to the regularity of their 
operations. But a machine which maintains, constructs, and re- 
produces itself is not a machine. In order to build such a machine 
we should have to possess the key of life, i. e., the understanding 
of the supposed, but by no means demonstrated, mechanics of liv- 
ing protoplasm. Everything points to the conclusion that the in- 
stinctive automatisms have been gradually acquired and heredita- 
rily fixed by natural selection and other factors of inheritance. But 
there are also secondary automatisms or habits which arise through 
the frequent repetition of plastic activities and are therefore espe- 
cially characteristic of man's enormous brain-development. 

In all the psychic provinces of intellect, feeling, and will, 
habits follow the constant law of perfection through repetition. 
Through practice every repeated plastic brain-activity gradually 
becomes automatic, becomes "second nature," i. e., similar to in- 
stinct. Nevertheless instinct is not inherited habit, but phylogenet- 
ically inherited intelligence which has gradually become adapted 
and crystalised by natural selection or by some other means. 

Plastic activity manifests itself, in general, in the ability of the 
nervous system to conform or adapt itself to new and unexpected 
conditions and also through its faculty of bringing about internally 
new combinations of neurocyme. Bethe calls this the power of 
modification. But since, notwithstanding his pretended issue with 
anthropomorphism, he himself continually proceeds in an anthro- 
pomorphic spirit and demands human ratiocination of animals, if 
they are to be credited with plasticity (power of modification), he 
naturally overlooks the fact that the beginnings of plasticity are 
primordial, that they are in fact already present in the Amoeba, 
which adapts itself to its environment. Nor is this fact to be con- 
jured out of the world by Loeb's word "tropisms." 

Automatic and plastic activities, whether simple or complex, 
are merely relative antitheses. They grade over into each other, 


e. g., in the formation of habits but also in instincts. In their ex- 
treme forms they resemble two terminal branches of a tree, but 
they may lead to similar results through so-called convergence of 
the conditions of life (slavery and cattle-keeping among ants and 
men). The automatic may be more easily derived from the plastic 
activities than vice versa. One thing is established, however: since 
a tolerably complicated plastic activity admits of many possibilities 
of adaptation in the individual brain, it requires much more nerv- 
ous substance, many more neurons, but has more resistances to 
overcome in order to attain a complicated result. The activities 
of an Amoeba belong therefore rather to the plasticity of living 
molecules, but not as yet to that of cooperating nerve-elements; as 
cell-plasticity it should really be designated as "undifferentiated." 1 
There are formed in certain animals specially complex automatisms, 
or instincts, which require relatively little plasticity and few neu- 
rons. In others, on the contrary, there remains relatively consider- 
able nerve-substance for individual plasticity, while the instincts 
are less complicated. Other animals, again, have little besides the 
lower reflex centers and are extremely poor in both kinds of com- 
plex activities. Still others, finally, are rich in both. Strong so- 
called "hereditary predispositions" or unfinished instincts consti- 
tute the phylogenetic transitions between both kinds of activity 
and are of extraordinarily high development in man. 

Spoken and especially written language, moreover, enable man 
to exploit his brain to a wonderful extent. This leads us to under- 
estimate animals. Both in animals and man the true value of the 
brain is falsified by training, i. e., artificially heightened. We 
overestimate the powers of the educated negro and the trained dog 
and underestimate the powers of the illiterate individual and the 
wild animal. 

I beg your indulgence for this lengthy introduction to my sub- 

1 If I expressly refrain from accepting the premature and unjustifiable identifi- 
cation of cell-life with a "machine," I nevertheless do not share the so-called vital- 
istic views. It is quite possible that science may sometime be able to produce liv- 
ing protoplasm from inorganic matter. The vital forces have undoubtedly origi- 
nated from physico-chemical forces. But the ultimate nature of the latter and of 
the assumed material atoms is, of course, metaphysical, i. e., unknowable. 


ject, but it seemed necessary that we should come to some under- 
standing concerning the validity of comparative psychology. My 
further task now consists in demonstrating to you what manner of 
psychical faculties may be detected in insects. Of course, I shall 
select in the first place the ants as the insects with which I am 
most familiar. Let us first examine the brain of these animals. 

In order to determine the psychical value of a central nervous 
system it is necessary, first, to eliminate all the nerve-centers which 
subserve the lower functions, above the immediate innervation of 
the muscles and sense-organs as first centers. The volume of such 
neuron-complexes does not depend on the intricacy of mental work 
but on the number of muscle-fibres concerned in it, the sensory 
surfaces, and the reflex apparatus, hence above all things on the 
size of the animals. Complex instincts already require the inter- 
vention of much more plastic work and for this purpose such nerve- 
centers alone would be inadequate. 

A beautiful example of the fact that complex mental combina- 
tions require a large nerve-center dominating the sensory and mus- 
cular centers is furnished by the brain of the ant. The ant-colony 
commonly consists of three kinds of individuals : the queen, or 
female (largest), the workers which are smaller, and the males 
which are usually larger than the workers. The workers excel in 
complex instincts and in clearly demonstrable mental powers 
(memory, plasticity, etc.). These are much less developed in the 
queens. The males are incredibly stupid, unable to distinguish 
friends from enemies and incapable of finding their way back to 
their nest. Nevertheless the latter have very highly developed 
eyes and antennae, i. e., the two sense-organs which alone are con- 
nected with the brain, or supra-oesophageal ganglion and enable 
them to possess themselves of the females during the nuptial flight. 
No muscles are innervated by the supra-oesophageal ganglion. 
These conditions greatly facilitate the comparison of the percep- 
tive organs, i. e., of the brain (corpora pedunculate?) in the three 
sexes. This is very large in the worker, much smaller in the fe- 
male, and almost vestigial in the male, whereas the optic and 
olfactory lobes are very large in the latter. The cortical portion 


of the large worker brain is, moreover, extremely rich in cellular 
elements. In this connection I would request you to glance at the 
figures and their explanation. 

Very recently, to be sure, it has come to be the fashion to un- 
derestimate the importance of brain-morphology in psychology and 
even in nerve-physiology. But fashions, especiall} 7 such absurd 
ones as this, should have no influence on true investigation. Of 
course, we should not expect anatomy to say what it was never in- 
tended to say. 

In ants, injury to the cerebrum leads to the same results as in- 
jury to the brain of the pigeon. 

In this place I would refer you for a fuller account of the de- 
tails of sensation and the psychic peculiarities of insects to my 
more extended work above mentioned : Sensations des Insectes. 

It can be demonstrated that insects possess the senses of 
sight, smell, taste, and touch. The auditory sense is doubtful. 
Perhaps a sense of touch modified for the perception of delicate 
vibrations may bear a deceptive resemblance to hearing. A sixth 
sense has nowhere been shown to occur. A photodermatic sense, 
modified for light-sensation, must be regarded as a form of the tac- 
tile sense. It occurs in many insects. This sense is in no respect 
of an optic nature. In aquatic insects the olfactory and gustatory 
senses perhaps grade over into each other somewhat (Nagel), since 
both perceive chemical substances dissolved in the water. 

The visual sense of the facetted eyes is especially adapted for 
seeing movements, i. e. , for perceiving relative changes of position 
in the retinal image. In flight it is able to localise'large spatial 
areas admirably, but must show less definite contours of the ob- 
jects than our eyes. The compound eye yields only a single up- 
right image (Exner), the clearness of which increases with the 
number of facets and the convexity of the eye. Exner succeeded 
in photographing this image in the fire-fly (Lampyris). As the 
eyes are immovable the sight of resting objects soon disappears so 
far as the resting insect is concerned. For this reason resting in- 
sects are easily captured when very slowly approached. In flight 
insects orient themselves in space by means of their compound 


Fig. W. 

Fig. F, 

Fig. M. 


Brain (supra-oesophageal ganglion) of an ant (Lasius fuliginosus), magnified 
60 diameters, seen from above. 

Fig. W. Brain of the Worker. 

Fig. F. Brain of the Queen (Female) 

Fig. M. Brain of the Male. 

St. = Brain trunk. L. op. =Lobus opticus (optic lobe). L. olf. = Lobus olfac- 
torius si ve antennalis (olfactory lobe). N. = Facetted eye. N. olf. =Nervus olfac- 
torius sive antennalis (olfactory nerve). O.= Ocelli, or simple eyes with their 
nerves (present only in the male and queen). H. = Cellular brain cortex (developed 
only in the worker and queen). C. p. = Corpora pedunculata, or fungiform bodies 
(developed only in the worker and queen). R. =Rudimental cortex of male. 

The length of the whole ant is : 

in the worker 4.5 mm ; 
in the queen 6.0 mm ; 
in the male 4.5 mm. 

N. B. The striation of the corpora pedunculata and their stems is represented 
diagrammatically, for the purpose of indicating rather coarsely their extremely 
delicate fibrillar structure. 


eyes. Odor, when perceived, merely draws these animals in a 
particular direction. When the compound eyes are covered, all 
powers of orientation in the air are lost. Many insects can adapt 
their eyes for the day or night by a shifting of the pigment. Ants 
see the ultra-violet with their eyes. Honey-bees and humble-bees 
can distinguish colors, but obviously in other tones than we do, 
since they cannot be deceived by artificial flowers of the most skil- 
ful workmanship. This may be due to admixtures of the ultra-violet 
rays which are invisible to our eyes. 

The ocelli (simple eyes) play a subordinate role, and probably 
serve as organs of sight for objects situated in the immediate vicin- 
ity and in dark cavities. 

The olfactory sense has its seat in the antennae, usually in the 
club-shaped flagellum, or rather in the pore-plates and olfactory 
rods of these portions of the antennas. On account of its external 
and moveable position at the tip of the antenna, the olfactory or- 
gan possesses two properties which are lacking in the vertebrates, 
and particularly in man. These are : 

1. The power of perceiving the chemical nature of a body by 
direct contact (contact-odor); 

2. The power of space-perception and of perceiving the form 
of objects and that of the animal's own trail by means of odor, and 
the additional property of leaving associated memories. 

The olfactory sense of insects, therefore, gives these animals 
definite and clear-cut perceptions of space-relations, and enables 
the animal while moving on the surface of the ground to orient it- 
self with facility. I have designated this sense, which is thus quali- 
tatively, i. e., in its specific energy, very different from our olfac- 
tory sense, as the topochemical (olfactory) sense. Probably the 
pore-plates are used for perceiving odor at a distance and the olfac- 
tory rods for contact-odor, but this is pure conjecture. Extirpation 
of the antennae destroys the power of distinguishing friends from 
enemies and deprives the ant of the faculty of orienting itself on 
the ground and of finding its way, whereas it is possible to cut off 
three legs and an antenna without seriously impairing these powers. 
The topochemical sense always permits the ant to distinguish be- 


tween the directions of its trail, a faculty which Bethe attributes to 
a mysterious polarisation. The ability to sense different odors 
varies enormously in different insects. An object possessing odor 
for one species is often odorless for other species (and for ourselves) 
and vice versa. 

The gustatory organs are situated on the mouth-parts. Among 
insects the reactions of this sense are very similar to our own. Will 
accustomed some wasps to look in a particular place for honey, 
which he afterwards mixed with quinine. The wasps detected the 
substance at once, made gestures of disgust, and never returned to 
the honey. Mixing the honey with alum had the same result. At 
first they returned, but after the disagreeable gustatory experience 
they failed to reappear. Incidentally this is also a proof of their 
gustatory memory and of their powers of association. 

Several organs have been found and described as auditory. 
But after their removal the supposed reaction to sounds persists. 
This would seem to indicate that a deceptive resemblance to hear- 
ing may be produced by the perception of delicate vibrations 
through the tactile sense (Duges). 

The tactile sense is everywhere represented by tactile hairs 
and papillae. It reacts more especially to delicate tremors of the 
atmosphere or soil. Certain arthropods, especially the spiders, 
orient themselves mainly by means of this sense. 

It may be demonstrated that insects, according to the species 
and conditions of life, use their different senses in combination for 
purposes of orienting themselves and for perceiving the external 
world. Many species lack eyes and hence also the sense of sight. 
In others, again, the olfactory sense is obtuse ; certain other forms 
lack the contact-odor sense (e. g., most Diptera). 

It has been shown that the superb powers of orientation ex- 
hibited by certain aerial animals, like birds (carrier-pigeons), bees, 
etc., depend on vision and its memories. Movement in the air 
gives this sense enormous and manifold values. The semi-circular 
canals of the auditory organ are an apparatus of equilibrium in 
vertebrates and mediate sensations of acceleration and rotation 
(Mach-Breuer), but do not give external orientation. For the dem- 


onstration of these matters I must refer you to my work above- 
cited. A specific, magnetic, or other mode of orientation, indepen- 
dent of the known senses, does not exist. 

The facts above presented constitute the basis of insect psy- 
cholog)'. The social insects are especially favorable objects for 
study on account of their manifold reciprocal relationships. If in 
speaking of their behavior I use terms borrowed from human life, 
I request you, once for all, to bear in mind that these are not to 
be interpreted in an anthropomorphic but in an analogous sense. 


Many insects (perhaps all, in a more rudimental condition) 
possess memory, i. e., they are able to store up sense-impressions 
in their brains for subsequent use. Insects are not merely attracted 
directly by sensory stimuli, as Bethe imagines. Huber, myself, 
Fabre, Lubbock, Wasmann, Von Buttel-Reepen, have demonstrated 
this fact experimentally. That bees, wasps, etc., can find their way 
in flight through the air, notwithstanding wind and rain (and hence 
under circumstances precluding the existence of any possible odor- 
iferous trail), and even after the antennae have been cut off, to a 
concealed place where they have found what they desired, though 
this place may be quite invisible from their nest, and this even 
after the expiration of days and weeks, is a fact of special impor- 
tance as proof of the above assertion. It can be shown that these 
insects recognise objects by means of their colors, their forms, and 
especially by their position in space. Position they perceive 
through the mutual relations and succession of the large objects in 
space, as these are revealed to them in their rapid change of place 
during flight in their compound eyes (shifting of retinal images). 
Especially the experiments performed by Von Buttel-Reepen and 
myself leave no doubt concerning this fact. Additional proof of a 
different nature is furnished by Von Buttel, who found that ether or 
chloroform narcosis deprives bees of all memory. By this means 
enemies can be converted into friends. Under these circumstances, 
too, all memory of locality is lost and must be reacquired by means 


of a new flight of orientation. An animal, however, certainly can- 
not forget without having remembered. 

The topochemical antennal sense also furnishes splendid proofs 
of memory in ants, bees, etc. An ant may perform an arduous 
journey of thirty meters from her ruined nest, there find a place 
suitable for building another nest, return, orienting herself by 
means of her antennae, seize a companion who forthwith rolls her- 
self about her abductrix, and is carried to the newly selected spot. 
The latter then also finds her way to the original nest, and both 
each carry back another companion, etc. The memory of the suit- 
able nature of the locality for establishing a new nest must exist in 
the brain of the first ant or she would not return, laden with a com- 
panion, to this very spot. The slave-making ants {Polyergus} un- 
dertake predatory expeditions, led by a few workers, who for days 
and weeks previously have been searching the neighborhood for 
nests of Formica fusca. The ants often lose their way, remain 
standing and hunt about for a long time till one or the other finds 
the topochemical trail and indicates to the others the direction to 
be followed by rapidly pushing ahead. Then the pupae of the For- 
mica fusca nest, which they have found, are brought up from the 
depths of the galleries, appropriated and dragged home, often a 
distance of forty meters or more. If the plundered nest still con- 
tains pupae, the robbers return on the same or following days and 
carry off the remainder, but if there are no pupae left they do not 
return. How do the Polyergus know whether there are pupae re- 
maining? It can be demonstrated that smell could not attract them 
from such a distance, and this is even less possible for sight or any 
other sense. Memory alone, i. e., the recollection that many pupae 
still remain behind in the plundered nest can induce them to re- 
turn. I have carefully followed a great number of these predatory 

While Formica species follow their topochemical trail with 
great difficulty over new roads, they nevertheless know the imme- 
diate surroundings of their nest so well that even shovelling away 
the earth can scarcely disconcert them, and they find their way at 
once, as Wasmann emphatically states and as I myself have often 


observed. That this cannot be due to smelling at long range can 
be demonstrated in another manner, for the olfactory powers of the 
genus Formica, like those of honey-bees, are not sufficiently acute 
for this purpose, as has been shown in innumerable experiments by 
all connoisseurs of these animals. Certain ants can recognise friends 
even after the expiration of months. In ants and bees there are 
very complex combinations and mixtures of odors, which Von But- 
tel has very aptly distinguished as nest-odor, colony- (family-) odor, 
and individual odor. In ants we have in addition a species-odor, 
while the queen-odor does not play the same role as among bees. 

It follows from these and many other considerations that the 
social Hymenoptera can store up in their brains visual images and 
topochemical odor-images and combine these to form perceptions 
or something of a similar nature, and that they can associate such 
perceptions, even those of different senses, especially sight, odor, 
and taste, with one another and thereby acquire spatial images. 

Huber as well as Von Buttel, Wasmann, and myself have 
always found that these animals, through frequent repetition of an 
activity, journey, etc., gain in the certainty and rapidity of the ex- 
ecution of their instincts. Hence they form, very rapidly to be 
sure, habits. Von Buttel gives splendid examples of these in the 
robber-bees, i. e., in some of the common honey-bees that have 
acquired the habit of stealing the honey from the hives of strangers. 
At first the robbers display some hesitation, though later they be- 
come more and more impudent. But he who uses the term habit, 
must imply secondary automatism and a pre-existing plastic adapt- 
ability. Von Buttel adduces an admirable proof of this whole mat- 
ter and at the same time one of the clearest and simplest refuta- 
tions of Bethe's innumerable blunders, when he shows that bees 
that have never flown from the hive, even though they may be 
older than others that have already flown, are unable to find their 
way back even from a distance of a few meters, when they are un- 
able to see the hive, whereas old bees know the whole environ- 
ment, often to a distance of six or seven kilometers. 

It results, therefore, from the unanimous observations of all 
the connoisseurs that sensation, perception, and association, infer- 


ence, memory and habit follow in the social insects on the whole 
the same fundamental laws as in the vertebrates and ourselves. 
Furthermore, attention is surprisingly developed in insects, often 
taking on an obsessional character and being difficult to divert. 

On the other hand, inherited automatism exhibits a colossal 
preponderance. The above-mentioned faculties are manifested 
only in an extremely feeble form beyond the confines of the in- 
stinct-automatism stereotyped in the species. 

An insect is extraordinarily stupid and inadaptable to all things 
not related to its instincts. Nevertheless I succeeded in teaching 
a water-beetle {Dytiscus marginalis} which in nature feeds only in 
the water, to eat on my table. While thus feeding, it always exe- 
cuted a clumsy flexor-movement with its fore-legs which brought it 
over on its back. The insect learned to keep on feeding while on 
its back, but it would not dispense with this movement, which is 
adapted to feeding in the water. On the other hand, it always at- 
tempted to leap out of the water (no longer fleeing to the bottom 
of the vessel) when I entered the room, and nibbled at the tip of 
my finger in the most familiar manner. Now these are certainly 
plastic variations of instinct. In a similar manner some large 
Algerian ants which I transplanted to Zurich, learned during the 
course of the summer months to close the entrance of their nest 
with pellets of earth, because they were being persecuted and an- 
noyed by our little Lasius niger. In Algiers I always saw the nest- 
opening wide open. There are many similar examples which go 
to show that these tiny animals can utilise some few of their expe- 
riences even when this requires a departure from the usual in- 

That ants, bees, and wasps are able to exchange communica- 
tions that are understood, and that they do not merely titillate one 
another with their antennae as Bethe maintains, has been demon- 
strated in so many hundred instances, that it is unnecessary to 
waste many words on this subject. The observations of a single 
predatory expedition of Polyergus, with a standing still of the whole 
army and a seeking for the lost trail, is proof sufficient of the above 
statement. But, of course, this is not language in the human sense ! 


There are no abstract concepts corresponding to the signs. We 
are here concerned only with hereditary, instinctively automatic 
signs. The same is true of their comprehension (pushing with the 
head, rushing at one another with wide-open mandibles, titillation 
with the antennae, stridulatory movement of the abdomen, etc.). 
Moreover, imitation plays a great role. Ants, bees, etc., imitate 
and follow their companions. Hence it is decidedly erroneous (and 
in this matter Wasmann, Von Buttel, and myself are of but one 
opinion) to inject human thought-conception and human ratiocina- 
tion into this instinct language, as has been done to some extent, 
at least, even by Pierre Huber, not to mention others. It is even 
very doubtful whether a so-called general sensory idea (i. e. , a gen- 
eral idea of an object, like the idea "ant," "enemy," "nest," 
"pupa") can arise in the emmet brain. This is hardly capable of 
demonstration. Undoubtedly perception and association can be 
carried on in a very simple way, after the manner of insects, with- 
out ever rising to such complex results. At any rate proofs of such 
an assumption are lacking. But what exists is surely in itself suffi- 
ciently interesting and important. It gives us at least an insight 
into the brain-life of these animals. 

Better than any generalisations, a good example will show 
what I mean. 

Plateau had maintained that when Dahlia blossoms are covered 
with green leaves, bees nevertheless return to them at once. At 
first he concealed his Dahlias incompletely (i. e., only their ray- 
florets), afterwards completely, but still in an unsatisfactory man- 
ner, and inferred from the results that bees are attracted by odor 
and not by sight. 

a. In a Dahlia bed visited by many bees and comprising about 
forty-three floral heads of different colors, I covered first seventeen 
and then eight at 2.15 P. M., September loth, with grape-leaves 
bent around them and fastened with pins. 

b. Of four I covered only the yellow disc ; 

c. Of one, on the other hand, I covered only the outer ray- 
florets, leaving the disc visible. 


So many bees were visiting the Dahlias that at times there 
were two or three to a flower. 

Result : Immediately all the completely covered flowers ceased 
to be visited by the bees. Dahlia (V) continued to be visited like 
those completely visible. The bees often flew to Dahlias (<5) but at 
once abandoned them ; a few, however, succeeded in finding the 
disc beneath the leaves. 

Then as soon as I removed the covering from a red Dahlia the 
bees at once flew to it ; and soon a poorly concealed specimen was 
detected and visited. Later an inquisitive bee discovered the en- 
trance to a covered Dahlia from the side or from below. Thence- 
forth this bee, but only this one, returned to this same covered 

Nevertheless several bees seemed to be seeking the Dahlias 
which had so suddenly disappeared. Towards 5.30 o'clock some 
of them had detected the covered flowers. Thenceforth these in- 
sects were rapidly imitated by the other bees, and in a short time 
the hidden flowers were again being visited. As soon as a bee had 
discovered my imposition and found the entrance to a hidden 
flower, she flew in her subsequent journeys, without hesitation to 
the concealed opening of the grape-leaf. As long as a bee had 
merely made the discovery by herself, she remained unnoticed by 
the others. When this was accomplished by several, however, (usu- 
ally by four or five,) the others followed their example. 

Plateau, therefore, conducted his experiments in a faulty man- 
ner and obtained erroneous results. The bees still saw the Dahlias 
which he at first incompletely concealed. Then, by the time he 
had covered them up completely, but only from above, they had 
already detected the fraud and saw the Dahlias also from the side. 
Plateau had failed to take into consideration the bee's memory and 

September i3th I made some crude imitations of Dahlias by 
sticking the yellow heads of Hieracium (hawkweed) each in a Pe- 
tunia flower, and placed them among the Dahlias. Neither the 
Petunias nor the Hieracium had been visited by the bees. Never- 
theless many of the honey and humble-bees flew at first to the arte- 


facts in almost as great numbers as to the Dahlias, but at once 
abandoned the flowers when they had detected the error, obviously 
by means of their sense of smell. The same results were produced 
by a Dahlia, the disc of which had been replaced by the disc of a 

As a control experiment I had placed a beautiful, odorous 
Dahlia disc among the white and yellow Chrysanthemums which 
had been neglected by the bees. For a whole half hour the bees 
flew by only a few centimeters above the disc without noticing it ; 
not till then was it visited by a bee that happened to be followed 
by a second. From this moment the Dahlia disc which lay in the 
path of flight was visited like the others, whereas on the other hand 
the Petunia-Hieracium artefacts, now known to be fraudulent, were 
no longer noticed. 

Plateau has demonstrated that artificial flowers, no matter how 
carefully copied from the human standpoint, are not noticed by in- 
sects. I placed artefacts of this description among the Dahlias. 
They remained in fact entirely neglected. Perhaps, as above sug- 
gested, the bees are able to distinguish the chlorophyll colors from 
other artificial hues, owing to admixtures of the ultra-violet rays, 
or by some other means. But since Plateau imagines that the arti- 
ficial flowers repel insects, I cut out, Sept. igth, the following 
rather crude paper-flowers : 

a. A red flower ; 

/3. A white flower ; 

y. A blue flower ; 

8 A blue flower, with a yellow center made from a dead leaf; 

c. A rose-colored piece of paper with a dry Dahlia disc ; 

. A green Dahlia leaf (unchanged). 

It was nine o'clock in the morning. I placed a drop of honey 
on each of the six artefacts mounted among the Dahlias. For a 
quarter of an hour many bees flew past, very close to my artefacts 
but without perceiving and hence without smelling the honey. I 
went away for an hour. On my return artefact 8 was without honey, 
and must therefore have been discovered by the bees. All the 
others had remained quite untouched and unnoticed. 


With some difficulty I next undertook to bring artefact a very 
close to a bee resting on a Dahlia. But the attention of the bee 
was so deeply engrossed by the Dahlia that I had to repeat the ex- 
periment four or five times till I succeeded in bringing the honey 
within reach of her proboscis. The insect at once began to suck 
tip the honey from the paper-flower. I marked the bee's back with 
blue paint so that I might be able to recognise her, and repeated 
the experiment with /? and e. In these cases one of the bees was 
painted yellow, the other white. 

Soon the blue bee, which had in the meantime gone to the 
hive, returned, flew at once to a, first hovering about it dubiously, 
then to 8, where she fed, then again to a, but not to the Dahlias. 
Later the yellow bee returned to (3 and fed, and flew to a and 8 
where she again fed, but gave as little heed to the Dahlias as did 
the blue bee. 

Thereupon the white bee returned seeking e, but failing to find 
it, at once went to feeding on some of the Dahlias. But she tarried 
only a moment on each Dahlia as if tortured by the id^e fixe of 
honey. She returned to the artefacts, the perception of which, 
however, she was not quite able to associate with the memory of 
the honey flavor. At last she found a separate piece of e, which 
happened to be turned down somewhat behind, and began lapping 
up the honey. 

Thenceforth the three painted bees, and these alone, returned 
regularly to the artefacts and no longer visited the Dahlias. The 
fact is of great importance that the painted bees entirely of their 
own accord, undoubtedly through an instinctive inference from 
analogy, discovered the other artefacts as soon as their attention 
had been attracted by the honey on one of them, notwithstanding 
the fact that the artefacts were some distance from one another and 
of different colors. For were not the Dahlias, too, which they had 
previously visited, of different colors? Thus the blue bee flew to 
a, (3, y, and 8, the yellow to j3, a, 8, and y, the white e, a, ft, and 8. 
Matters continued thus for half an hour. The hidden green was 
not found, evidently because it was indistinguishable from the green 


Finally one bee, by herself, having had in all probability her 
attention attracted by the three others, came to 8 and fed. I marked 
her with carmine. Thereupon she flew to a and drove the blue bee 
away. Another bee was attracted to c of her own accord and was 
painted with cinnobar. Still another bee came by herself to /3 and 
was painted green. It was now 12.30 o'clock. The experiment 
had therefore lasted more than three hours, and during this time 
only six bees had come to know the artefacts, while the great ma- 
jority still kept on visiting the Dahlias. But now the other bees 
began to have their attention attracted by the visitors to the arte- 
facts. One, then two, then three, and finally more new ones fol- 
lowed, and I had not sufficient colors with which to mark them. 
Every moment I was obliged to replenish the honey. Then I went 
to dinner and returned at 1.25. At this moment seven bees were 
feeding on ft, two on a, one on y, three on 8, the white one alone 
on e. More than half of all these were new, unpainted followers. 
Now a veritable swarm of bees threw themselves on the artefacts 
and licked up the last traces of the honey. Then for the first time, 
after more than four hours, a bee from the swarm discovered the 
honey on the artefact , which on account of its color had remained 
concealed up to this time ! 

As a pack of hounds throws itself on an empty skeleton, the 
swarm of bees, now completely diverted from the Dahlias, cast 
themselves on the completely empty artefacts and vainly searched 
every corner of them for honey. It was 1.55 P. M. The bees be- 
gan to scatter and return to the Dahlias. Then I replaced a and 
ft by a red and white paper respectively, which had never come in 
contact with honey and could not therefore smell of the substance. 
These pieces of paper, nevertheless, were visited and examined by 
various bees, whose brains were still possessed with the fixed idea 
of the flavor of honey. The white bee, e. g., investigated the white 
paper very carefully for a period of three to four minutes. There 
could, of course, be no such thing as an unknown force or attrac- 
tion of odor, or brilliancy of floral colors. This fact can only be 
explained by an association of space, form, and color memories with 
memories of taste. 


Thereupon I took all the artefacts in my left hand for the pur- 
pose of carrying them away. Two or three bees followed me, hov- 
ering about my left hand, and tried to alight on the empty artefacts. 
The space-image had changed and only the color and form could 
any longer be of service to the bees in their recognition of these 

This experiment is so clear and unequivocal that I mention it 
here among many others. It demonstrates : 

1. The space, form, and color perceptions of the honey-bee. 
That these are possible only through the agency of the compound 
eyes is proved by other experiments (varnishing the eyes, extirpa- 
tion of the antennae, mouth-parts, etc.). 

2. The memory of the honey-bee, in particular her visual and 
gustatory memory. 

3. Her power of associating gustatory with visual memories. 

4. Her ability instinctively to draw inferences from analogy : 
If she has once been offered honey in an artefact, she will investi- 
gate others, even those of a different color and hitherto unnoticed. 
These she compares by means of the visual sense, since they are 
relatively similar, and recognises them as similar though such ob- 
jects are most unusual in the bee's experience. 

5. Her poor olfactory sense, which is useful only at very close 

6. The onesidedness and narrow circle of her attention. 

7. The rapid formation of habits. 

8. The limits of imitation of bees by one another. 

Of course, I should not allow myself to draw these conclusions 
from a single experiment, if they had not been confirmed by in- 
numerable observations by the ablest investigators in this field. 
Lubbock showed clearly that it is necessary to train a bee for some 
time to go to a particular color if one wishes to compel her to pay 
no attention to other colors. This is the only way in which it is 
possible to demonstrate her ability to distinguish colors. My bees, 
on the contrary, had been trained on differently colored objects 
(Dahlias and artefacts) and therefore paid no attention to differ- 
ences in color. It would be a fallacy to conclude from this that 


they do not distinguish colors. On the contrary, by means of other 
experiments I have fully confirmed Lubbock's results. 

By 2. 20 P. M. all of my bees, even the painted ones, had re- 
turned to the Dahlias. 

On September 27, a week later, I wished to perform a fresh 
experiment with the same bees. I intended to make them distin- 
guish between differently colored discs, placed at different points on 
a long scale, representing on a great sheet of paper, varying intensi- 
ties of light from white through gray to black. First, I wished to 
train a bee to a single color. But I had calculated without the 
bee's memory, which rendered the whole experiment impracticable. 
Scarcely had I placed my paper with the discs on the lawn near 
the Dahlia bed, and placed one or two bees on the blue discs and 
marked them with colors, when they began to investigate all the 
red, blue, white, black and other discs with or without honey. After 
a few moments had elapsed, other bees came from the Dahlia bed 
and in a short time a whole swarm threw itself on the paper discs. 
Of course, those that had been provided with honey were most vis- 
ited, because they detained the bees, but even the discs without 
honey were stormed and scrutinised by bees following one another 
in their flight. The bees besieged even the paint-box. Among 
these there was one that I had previously deprived of her antennae. 
She had previously partaken of the honey on the blue discs and 
had returned to the hive. This bee , examined the blue piece of 
paint in the color-box. 

In brief, my experiment was impossible, because all the bees 
still remembered from a former occasion the many-colored artefacts 
provided with honey, and therefore examined all the paper discs 
no matter of what color. The association between the taste of the 
honey and the paper discs had been again aroused by the sight- 
perception of the latter, and had acquired both consistency and 
rapid and powerful imitation, because honey happened to be actually 
found on some of the discs. 

Together with the perceptive and associative powers, the 
power of drawing simple, instinctive inferences from analogy is 
also apparent. Without this, indeed, the operation of perception 


and memory would be inconceivable ! We have just given an ex- 
ample. I have shown on a former occasion that humble-bees, 
whose nest I had transferred to my window, when they returned 
home often confounded other windows of the same fa9ade and ex- 
amined them for a long time before they discovered the right one. 
Lubbock reports similar facts. Von Buttel shows that bees that 
are accustomed to rooms and windows, learn to examine the rooms 
and windows in other places, i. e., other houses. When Pissot 
suspended wire netting with meshes twenty-two mm. in diameter 
in front of a wasp nest, the wasps hesitated at first, then went 
around the netting by crawling along the ground or avoided it in 
some other way. But they soon learned to fly directly through the 
meshes. The sense of sight, observed during flight, is particularly 
well adapted to experiments of this kind, which cannot therefore 
be performed with ants. But the latter undoubtedly draw similar 
inferences from the data derived from their topochemical antennal 
sense. The discovery of prey or other food on a plant or an ob- 
ject induces these insects to examine similar plants or objects and 
to perform other actions of a like nature. 

There are, on the other hand, certain very stupid insects, like 
the males of ants, the Diptera and may-flies (Ephemerids) with 
rudimental brains, incapable of learning anything or of combining 
sense-impressions to any higher degree than as simple automatisms, 
and without any demonstrable retention of memory-images. Such 
insects lead a life almost exclusively dominated by sensory stimuli; 
but their lives are adapted to extremely simple conditions. In 
these very instances the difference is most striking, and they dem- 
onstrate most clearly through comparison and contrast the plus 
possessed by more intelligent insects. 


The notion of volition, in contradistinction to the notion of 
reflex action, presupposes the expiration of a certain time interval 
and the operation of mediating and complex brain-activities be- 
tween the sense-impression and the movement which it conditions. 
In the operation of the purposeful automatisms of instinct which 


arouse one another into activity in certain sequences, there is also 
a time interval, filled out by internal, dynamic brain-processes as 
in the case of the will. Hence these are not pure reflexes. They 
may for a time suffer interruption and then be again continued. 
But their operation is brought about in great measure by a con- 
catenation of complicated reflexes which follow one another in a 
compulsory order. On this account the term automatism or in- 
stinct is justifiable. 

If we are to speak of will in the narrower sense, we must be 
able to establish the existence of individual decisions, which can be 
directed according to circumstances, i. e., are modifiable, and may, 
for a certain period, remain dormant in the brain to be still per- 
formed notwithstanding. Such volition may be very different from 
the complex volition of man, which consists of the resultants of 
prodigiously manifold components that have been long preparing 
and combining. The ants exhibit positive and negative volitional 
phenomena, which cannot be mistaken. The ants of the genus 
Formica Linn are particularly brilliant in this respect, and they 
also illustrate the individual psychical activities most clearly. The 
above-mentioned migrations from nest to nest show very beauti- 
fully the individual plans of single workers carried out with great 
tenacity. For hours at a time an ant may try to overcome a multi- 
tude of difficulties for the purpose of attaining an aim which she 
has set herself. This aim is not accurately prescribed by instinct, 
as the insect may be confronted with several possibilities, so that 
it often happens that two ants may be working in opposition to 
each other. This looks like stupidity to the superficial observer. 
But it is just here that the ant's plasticity reveals itself. For a 
time the two little animals interfere with each other, but finally 
they notice the fact, and one of them gives in, goes away, or assists 
the other. 

These conditions are best observed during the building of nests 
or roads, e. g., in the horse-ant {Formica rufa) and still better in 
P. pratensis. It is necessary, however, to follow the behavior of a 
few ants for hours, if one would have a clear conception of this 
matter, and for this much patience and much time are necessary. 


The combats between ants, too, show certain very consistent aims 
of behavior, especially the struggles which I have called chronic 
combats (combats dfroid}. After two parties (two colonies brought 
together) have made peace with each other, one often sees a few 
individuals persecuting and maltreating certain individuals of the 
opposite party. They often carry their victims a long distance off, 
for the purpose of excluding them from the nest. If the ant that 
has been borne away returns to the nest and is found by her perse- 
cutrix, she is again seized and carried away to a still greater dis- 
tance. In one such case in an artificial nest of a small species of 
Leptothorax, the persecuting ant succeeded in dragging her victim 
to the edge of my table. She then stretched out her head and 
allowed her burden to fall on the floor. This was not chance, for 
she repeated the performance twice in succession after I had again 
placed the victim on the table. Among the different individuals of 
the previously hostile, but now pacified opposition, she had con- 
centrated her antipathy on this particular ant and had tried to make 
her return to the nest impossible. One must have very strong pre- 
conceived opinions if in such and many similar cases one would 
maintain that ants are lacking in individual decision and execution. 
Of course, all these things happen within the confines of the in- 
stinct-precincts of the species, and the different stages in the exe- 
tion of a project are instinctive. Moreover, I expressly defend my- 
self against the imputation that I am importing human reflection 
and abstract concepts into this volition of the ant, though we must 
honestly admit, nevertheless, that in the accomplishment of our 
human decisions both hereditary and secondary automatisms are 
permitted to pass unnoticed. While I am writing these words, my 
eyes operate with partially hereditary, and my hand with secondary 
automatisms. But it goes without saying that only a human brain 
is capable of carrying out my complex innervations and my con- 
comitant abstract reflections. But the ant must, nevertheless, as- 
sociate and consider somewhat in a concrete way after the manner 
of an ant, when it pursues one of the above-mentioned aims and 
combines its instincts with this special object in view. While, 
however, the instinct of the ant can be combined for only a few 


slightly different purposes, by means of a small number of plastic 
adaptations or associations, individually interrupted in their con- 
catenation or vice versa, in the thinking human being both inherited 
and secondary automatisms are only fragments or instruments in 
the service of an overwhelming, all-controlling, plastic brain-activ- 
ity. It may be said incidentally that the relative independence of 
the spinal chord and of subordinate brain-centers in the lower ani- 
mals (and even in the lower mammals) as compared with the cere- 
brum, may be explained in a similar manner if they are compared 
with the profound dependence of these organs and their functions 
on the massive cerebrum in man and even to some extent in the 
apes. The cerebrum splits up and controls its automatisms {divide 
et imp era}. 

While success visibly heightens both the audacity and tenacity 
of the ant-will, it is possible to observe after repeated failure or in 
consequence of the sudden and unexpected attacks of powerful en- 
emies a form of abulic dejection, which may lead to a neglect of 
the most important instincts, to cowardly flight, to the devouring 
or casting away of offspring, to neglect of work, and similar condi- 
tions. There is a chronically cumulative discouragement in degen- 
erate ant-colonies and an acute discouragement when a combat is 
lost. In the latter case one may see troops of large powerful ants 
fleeing before a single enemy, without even attempting to defend 
themselves, whereas the latter a few moments previously would 
have been killed by a few bites from the fleeing individuals. It is 
remarkable how soon the victor notices and utilises this abulic dis- 
couragement. The dejected ants usually rally after the flight and 
soon take heart and initiative again. But they offer but feeble re- 
sistance, e. g., to a renewed attack from the same enemy on the 
following day. Even an ant's brain does not so soon forget the 
defeats which it has suffered. 

In bitter conflicts between two colonies of nearly equal strength 
the tenacity of the struggle and with it the will to conquer increases 
till one of the parties is definitively overpowered. In the realm of 
will imitation plays a great role. Even among ants protervity and 
dejection are singularly contagious. 



It may perhaps sound ludicrous to speak of feelings in insects. 
But when we stop to consider how profoundly instinctive and 
fixed is our human life of feeling, how pronounced are the emotions 
in our domestic animals, and how closely interwoven with the im- 
pulses, we should expect to encounter emotions and feelings in 
animal psychology. And these may indeed be recognised so clearly 
that even Uexkuell would have to capitulate if he should come to 
know them more accurately. We find them already interwoven 
with the will as we have described it. Most of the emotions of in- 
sects are profoundly united to the instincts. Of such a nature is 
the jealousy of the queen bee when she kills the rival princesses, 
and the terror of the latter while they are still within their cells ; 
such is the rage of fighting ants, wasps, and bees, the above-men- 
tioned discouragement, the love of the brood, the self-devotion of 
the worker honey-bees, when they die of hunger while feeding their 
queen, and many other cases of a similar description. But there 
are also individual emotions that are not compelled altogether by 
instinct, e. g., the above-mentioned mania of certain ants for mal- 
treating some of their antagonists. On the other hand, as I have 
shown, friendly services (feeding), under exceptional circum- 
stances, may call forth feelings of sympathy and finally of partner- 
ship, even between ants of differents species. Further than this, 
feelings of sympathy, antipathy, and anger among ants may be in- 
tensified by repetition and by the corresponding activities, just as 
in other animals and man. 

The social sense of duty is instinctive in ants, though they ex- 
hibit great individual, temporary, and occasional deviations, which 
betray a certain amount of plasticity. 


I have rapidly reviewed the three main realms of ant-psychol- 
ogy. It is self-evident that in this matter they no more admit of 


sharp demarcation from one another than elsewhere. The will 
consists of centrifugal resultants of sense-impressions and feelings 
and in turn reacts powerfully on both of these. 

It is of considerable interest to observe the antagonism be- 
tween different perceptions, feelings, and volitions in ants and 
bees, and the manner in which in these animals the intensely fixed 
(obsessional) attention may be finally diverted from one thing to 
another. Here experiment is able to teach us much. While bees 
are busy foraging on only one species of flower, they overlook 
everything else, even other flowers. If their attention is diverted 
by honey offered them directly, although previously overlooked, 
they have eyes only for the honey. An intense emotion, like the 
swarming of honey-bees (von Buttel) compells these insects to 
forget all animosities and even the old maternal hive to which they 
no longer return. But if the latter happens to be painted blue, 
and if the swarming is interrupted by taking away the queen, the 
bees recollect the blue color of their old hive and fly to hives that 
are painted blue. Two feelings often struggle with each other in 
bees that are "crying" and without a queen: that of animosity 
towards strange bees and the desire for a queen. Now if they be 
given a strange queen by artificial means, they kill or maltreat her, 
because the former feeling at first predominates. For this reason 
the apiarist encloses the strange queen in a wire cage. Then the 
foreign odor annoys the bees less because it is further away and 
they are unable to persecute the queen. Still they recognise the 
specific queen-odor and are able to feed her through the bars of the 
cage. This suffices to pacify the hive. Then the second feeling 
quickly comes to the front ; the workers become rapidly inured to 
the new odor and after three or four days have elapsed, the queen 
may be liberated without peril. 

It is possible in ants to make the love of sweets struggle with 
the sense of duty, when enemies are made to attack a colony and 
honey is placed before the ants streaming forth to defend their 
nest. I have done this with Formica pratensis. At first the ants 
partook of the honey, but only for an instant. The sense of duty 
conquered and all of them without exception, hurried forth to battle 


and most of them to death. In this case a higher decision of in- 
stinct was victorious over the lower impulse. 

In r/sumJ I would lay stress on the following general conclu- 
sions : 

1. From the standpoint of natural science we are bound to 
hold fast to the psychophysiological theory of identity (Monism) in 
contradistinction to dualism, because it alone is in harmony with 
the facts and with the law of the conservation of energy. 

Our mind must be studied simultaneously both directly from 
within and indirectly from without, through biology and the condi- 
tions of its origin. Hence there is such a thing as comparative 
psychology of other individuals in addition to that of self, and in 
like manner we are led to a psychology of animals. Inference from 
analogy, applied with caution, is not only permissible in this sci- 
ence, but obligatory. 

2. The senses of insects are our own. Only the auditory sense 
still remains doubtful, so far as its location and interpretation are 
concerned. A sixth sense has not yet been shown to exist, and a 
special sense of direction and orientation is certainly lacking. The 
vestibular apparatus of vertebrates is merely an organ of equilibra- 
tion and mediates internal sensations of acceleration, but gives no 
orientation in space outside of the body. On the other hand the 
visual and olfactory senses of insects present varieties in the range 
of their competency and in their specific energies (vision of ultra- 
violet, functional peculiarities of the facetted eye, topochemical 
antennal sense and contact-odor). 

3. Reflexes, instincts, and plastic, individually adaptive, cen- 
tral nervous activities pass over into one another by gradations. 
Higher complications of these central or psychic functions corre- 
spond to a more complicated apparatus of superordinated neuron- 
complexes (cerebrum). 

4. Without becoming antagonistic, the central nervous activ- 
ity in the different groups and species of animals complicates itself 
in two directions : (#) through inheritance (natural selection, etc.) 
of the complex, purposeful automatisms, or instincts ; (l>) through 
the increasingly manifold possibilities of plastic, individually adap- 


tive activities, in combination with the faculty of gradually devel- 
oping secondary individual automatisms (habits). 

The latter mode requires many more nerve-elements. Through 
hereditary predispositions (imperfect instincts) of greater or less 
stability, it presents transitions to the former mode. 

5. In social insects the correlation of more developed psychic 
powers with the volume of the brain may be directly observed. 

6. In these animals it is possible to demonstrate the existence 
of memory, associations of sensory images, perceptions, attention, 
habits, simple powers of inference from analogy, the utilisation of 
individual experiences and hence distinct, though feeble, plastic, 
individual deliberations or adaptations. 

7. It is also possible to detect a corresponding, simpler form 
of volition, i. e., the carrying out of individual decisions in a more 
or less protracted time-sequence, through different concatenations 
of instincts ; furthermore different kinds of discomfort and pleasure 
emotions, as well as interactions and antagonisms between these di- 
verse psychic powers. 

8. In insect behavior the activity of the attention is one-sided 
and occupies a prominent place. It narrows the scope of behavior 
and renders the animal temporarily blind (inattentive) to other 

Thus, however different may be the development of the auto- 
matic and plastic, central neurocyme activities in the brains of dif- 
ferent animals, it is surely possible, nevertheless, to recognise cer- 
tain generally valid series of phenomena and their fundamental 

Even to-day I am compelled to uphold the seventh thesis 
which I established in 1877 in my habilitation as privat-docent in 
the University of Munich : 

"All the properties of the human mind may be derived from 
the properties of the animal mind." 

I would merely add to this : 

"And all the mental attributes of higher animals may be de- 
rived from those of lower animals." In other words: The doctrine 
of evolution is quite as valid in the province of psychology as it is 


in all the other provinces of organic life. Notwithstanding all the 
differences presented by animal organisms and the conditions of 
their existence, the psychic functions of the nerve-elements seem 
nevertheless, everywhere to be in accord with certain fundamental 
laws, even in the cases where this would be least expected on ac- 
count of the magnitude of the differences. 


Our sense of smell, like our sense of taste, is a chemical sense. 
But while the latter reacts only to substances dissolved in liquids 
and with but few (about five) different principal qualities, the 
olfactory sense reacts with innumerable qualities to particles of the 
most diverse substances dissolved in the atmosphere. Even to our 
relatively degenerate human olfactories, the number of these odor- 
qualities seems to be almost infinite. 

In insects that live in the air and on the earth the sense of 
taste seems to be located, not only like our own, in the mouth- 
parts, but also to exhibit the same qualities and the corresponding 
reactions. At any rate it is easy to show that these animals are 
usually very fond of sweet, and dislike bitter things, and that they 
perceive these two properties only after having tasted of the re- 
spective substances. F. Will, in particular, has published good 
experiments on this subject. 

In aquatic insects the conditions are more complicated. Nagel, 
who studied them more closely, shows how difficult it is in these 
cases to distinguish smell from taste, since substances dissolved in 
water are more or less clearly perceived or discerned from a dis- 
tance by both senses and sought or avoided in consequence. Nagel, 
at any rate, succeeded in showing that the palpi, which are of less 
importance in terrestrial insects, have an important function in 
aquatic forms. 

In this place we are concerned with an investigation of the 
sense of smell in terrestrial insects. Its seat has been proved to be 


in the antennae. A less important adjunct to these organs is located, 
as Nagel and Wasmann have shown, in the palpi. In the antennae 
it is usually the club or foliaceous or otherwise formed dilatations 
which accommodate the cellular ganglion of the antennary nerve. 
I shall not discuss the histological structure of the nerve-termina- 
tions but refer instead to Hicks, Leydig, Hauser, my own investi- 
gations and the other pertinent literature, especially to K. Kraepe- 
lin's excellent work. I would merely emphasise the following 
points : 

1. All the olfactory papillae of the antennae are transformed, 
hair-like pore-canals. 

2. All of these present a cellular dilatation just in front of the 

3. Tactile hairs are found on the antennae together with the 
olfactory papillae. 

4. The character and form of the nerve-terminations are highly 
variable, but they may be reduced to three principal types: pore- 
plates, olfactory rods, and olfactory hairs. The two latter are 
often nearly or quite indistinguishable from each other. The nerve- 
termination is always covered with a cuticula which may be never 
so delicate. 

Other end-organs of the Hymenopteran antenna described by 
Hicks and myself, are still entirely obscure, so far as their function 
is concerned, but they can have nothing to do with the sense of 
smell, since they are absent in insects with a delicate sense of smell 
(wasps) and accur in great numbers in the honey-bees, which have 
obtuse olfactories. 

That the antennae and not the nerve-terminations of the mouth 
and palate function, as organs of smell, has been demonstrated by 
my control experiments, which leave absolutely no grounds for 
doubt and have, moreover, been corroborated on all sides. Ter- 
restrial insects can discern chemical substances at a distance by 
means of their antennae only. But in touch, too, these organs are 
most important and the palpi only to a subordinate extent, namely 
in mastication. The antennae enable the insect to perceive the 
chemical nature of bodies and in particular, to recognise and dis- 


tinguish plants, other animals and food, except in so far as the 
visual and gustatory senses are concerned in these activities. These 
two senses may be readily eliminated, however, since the latter 
functions only during feeding and the former can be removed by 
varnishing the eyes or by other means. Many insects, too, are 
blind and find their way about exclusively by means of their an- 
tennae. This is the case, e. g. , with many predatory ants of the 
genus Eciton. 

But I will here assume these questions to be known and an- 
swered, nor will I indulge in polemics with Bethe and his asso- 
ciates concerning the propriety of designating the chemical anten- 
nal sense as "smell." I have discussed this matter elsewhere. 1 
What I wish to investigate in this place is the psychological quality 
of the antennal olfactory sense, how it results in part from observa- 
tion and in part from the too little heeded correlative laws of the 
psychological exploitation of each sense in accordance with its 
structure. I assume as known the doctrines of specific energies 
and adequate stimuli, together with the more recent investigations 
on the still undifferentiated senses, like photodermatism and the 
like, and would refer, moreover, to Helmholtz's Die Thatsachen in 
der Wahrnehmung, 1879. Hirschwald, Berlin. 

When in our own human subjective psychology, which alone 
is known to us directly, we investigate the manner in which we in- 
terpret our sensations, we happen upon a peculiar fact to which 
especially Herbert Spencer has called attention. We find that so- 
called perceptions consist, as is well known, of sensations which 
are bound together sometimes firmly, sometimes more loosely. The 
more intimately the sensations are bound together to form a whole, 
the easier it is for us to recall in our memory the whole from a 
part. Thus, e. g., it is easy for me to form an idea from the thought 
of the head of an acquaintance as to the remainder of his body. In 
the same manner the first note of a melody or the first verse of a 
poem brings back the remainder of either. But the thought of an 

1 " Sensations des Insectes," Rivista di Biologia Generate. Como, 1900-1901. 
For the remainder see also A. Forel, Mitth. des Munchener entom. Vereins, 1878, 
and Recueil. Zool. Suisse, 1886-1887. 


odor of violets, a sensation of hunger, or a stomach-ache, are in- 
capable of recalling in me either simultaneous or subsequent odors 
or feelings. 

These latter conditions call up in my consciousness much 
more easily certain associated visual, tactile, or auditory images 
(e. g., the visual image of a violet, a table set for a meal). As 
ideas they are commonly to be represented in consciousness only 
with considerable difficulty, and sometimes not at all, and they are 
scarcely capable of association among themselves. We readily ob- 
serve, moreover, that visual images furnish us mainly with space 
recollections, auditory images with sequences in time, and tactile 
images with both, but less perfectly. These are indubitable and 
well-known facts. 

But when we seek for the wherefore of these phenomena, we 
find the answer in the structure of the particular sense-organ and 
in its manner of functioning. 

It is well known that the eye gives us a very accurate image 
of the external world on our retina. Colors and forms are there 
depicted in the most delicate detail, and both the convergence of 
our two eyes and their movement and accommodation gives us be- 
sides the dimensions of depth through stereoscopic vision. What- 
ever may be still lacking or disturbing is supplied by instinctive 
inferences acquired by practice, both in memory and direct per- 
ception (like the lacunae of the visual field), or ignored (like the 
turbidity of the corpus vitreum). But the basis of the visual im- 
age is given in the coordinated tout ensemble of the retinal stimuli, 
namely the retinal image. 1 Hence, since the retina furnishes us 
with such spatial projections, and these in sharp details, or rela- 
tions, definitely coordinated with one another, the sense of sight 
gives us knowledge of space. For this reason, also, and solely on 
this account, we find it so easy to supply through memory by asso- 

1 It is well known that in this matter the movements of the eyes, the move- 
ments of the body and of external objects play an essential part, so that without 
these the eye would fail to give us any knowledge of space. But I need not discuss 
this further, since the antenna? of ants are at least quite as moveable and their 
olfactory sense is even more easily educated in unison with the tactile sense. 


elation the missing remnant of a visual spatial image. For this 
reason, too, the visual sensations are preeminently associative or 
relational in space, to use Spencer's expression. For the same 
reason the insane person so readily exhibits halucinations of com- 
plicated spatial images in the visual sphere. This would be im- 
possible in the case of the olfactory sense. 

Similarly, the organ of Corti in the ear gives us tone or sound 
scales in accurate time-sequence, and hence also associations of 
sequence much more perfectly than the other senses. Its associa- 
tions are thus in the main associations of sequence, because the 
end-apparatus registers time-sequences in time-intervals and not 
as space images. 

The corresponding cortical receptive areas are capable, in the 
first instance, merely of registering what is brought to them by the 
sense-stimuli and these are mainly associated spatial images for 
sight and tone or sound-sequences for hearing. 

Let us consider for a moment how odors strike the mucous 
membranes of our choanae. They are wafted towards us as wild 
mixtures in an airy maelstrom, which brings them to the olfactory 
terminations without order in the inhaled air or in the mucous of 
the palate. They come in such a way that there cannot possibly 
be any spatial association of the different odors in definite relation- 
ships. In time they succeed one another slowly and without order, 
according to the law of the stronger element in the mixture, but 
without any definite combination. If, after one has been inhaling 
the odor of violets, the atmosphere gradually becomes charged 
with more roast meat than violet particles, the odor of roast suc- 
ceeds that of violet. But nowhere can we perceive anything like a 
definitely associated sequence, so that neither our ideas of time nor 
those of space comprise odors that revive one another through as- 
sociation. By much sniffing of the surface of objects we could at 
most finally succeed in forming a kind of spatial image, but this 
would be very difficult owing to man's upright posture. Neverthe- 
less it is probable that dogs, hedge-hogs, and similar animals ac- 
quire a certain olfactory image by means of sniffing. The same 
conditions obtain in the sphere of taste and the visceral sensations 


for the same reasons. None of these senses furnish us with any 
sharply defined qualitative relations either in space or time. On 
this account they furnish by themselves no associations, no true 
perceptions, no memory images, but merely sensations, and these 
often as mixed sensations, which are vague and capable of being 
associated only with associative senses. The hallucinations of 
smell, taste, and of the splanchnic sensations, are not deceptive 
perceptions, since they cannot have a deceptive resemblance to ob- 
jects. They are simply paraesthesias or hyperaesthesias, i. e., path- 
ological sensations of an elementary character either without ade- 
quate stimulus or inadequate to the stimulus. 

The tactile sense furnishes us with a gross perception of space 
and of definite relations, and may, therefore, give rise to hallucina- 
tions, or false perceptions of objects. By better training its asso- 
ciative powers in the blind may be intensified. The visual sensa- 
tions are usually associated with tactile localisations. 

Thus we see that there is a law according to which the psy- 
chology of a sense depends not only on its specific energy but also 
on the manner in which it is able to transmit to the brain the rela- 
tions of its qualities in space and time. On this depends the 
knowledge we acquire concerning time and space relations through 
a particular sense and hence also its ability to form perceptions 
and associations in the brain. More or less experience is, of course, 
to be added or subtracted, but this is merely capable of enriching 
the knowledge of its possessor according to the measure of the re- 
lations of the particular sense-stimuli in space and time. 

I would beg you to hold fast to what I have said and then to 
picture to yourselves an olfactory sense, i. e. , a chemical sense 
effective at a distance and like our sense of smell, capable of re- 
ceiving impressions from particles of the most diverse substances 
diffused through the atmosphere, located not in your nostrils, but 
on your hands. For of such a nature is the position of the olfac- 
tory sense on the antennal club of the ant. 

Now imagine your olfactory hands in continual vibration, touch- 
ing all objects to the right and to the left as you walk along, thereby 
rapidly locating the position of all odoriferous objects as you ap- 


proach or recede from them, and perceiving the surfaces both simul- 
taneously and successively as parts of objects differing in odor and 
position. It is clear from the very outset that such sense-organs 
would enable you to construct a veritable odor-chart of the path 
you had traversed and one of double significance : 

1. A clear contact-odor chart, restricted, to be sure, to the 
immediate environment and giving the accurate odor-form of the 
objects touched (round odors, rectangular odors, elongate odors, 
etc.) and further hard and soft odors in combination with the tac- 
tile sensations. 

2. A less definite chart which, however, has orienting value 
for a certain distance, and produces emanations which we may pic- 
ture to ourselves like the red gas of bromine which we can actually 

If we have demonstrated that ants perceive chemical qualities 
through their antennae both from contact and from a distance, then 
the antennas must give them knowledge of space, if the above for- 
mulated law is true, and concerning this there can be little doubt. 
This must be true even from the fact that the two antennae simul- 
taneously perceive different and differently odoriferous portions of 
space. 1 

They must therefore also transmit perceptions and topograph- 
ically associated memories concerning a path thus touched and 
smelled. Both the trail of the ants themselves and the surround- 
ing objects must leave in their brains a chemical (odor-) space- 
form with different, more or less definitely circumscribed qualities, 
i. e., an odor-image of immediate space, and this must render as- 
sociated memories possible. Thus an ant must perceive the forms 
of its trail by means of smell. This is impossible, at least for the 
majority of the species, by means of the eyes. If this is true, an 
ant will always be able, no matter where she may be placed on her 

1 It is not without interest to compare these facts with Condillac's discussion 
( Treatise on the Sensations} concerning his hypothetical statue. Condillac shows 
that our sense of smell is of itself incapable of giving us space knowledge. But it 
is different in the case of the topochemical sense of smell in combination with the 
antennary movements. Here Condillac's conditions of the gustatory sense are ful- 


trail, to perceive what is to the right, left, behind or before her, 
and consequently what direction she is to take, according to whether 
she is bound for home, or in the opposite direction to a tree in- 
fested with Aphides, or the like. 

Singularly enough, I had established this latter fact in my 
"Etudes Myrme'cologiques en 1886" {Annales de la Societt Ento- 
mologique de Belgique} before I had arrived at its theoretical inter- 
pretation. But I was at once led by this discovery in the same 
work to the interpretation just given. Without knowing of my 
work in this connection, A. Bethe has recently established (dis- 
covered, as he supposes) this same fact, and has designated it as 
"polarisation of the ant-trail." He regards this as the expression 
of a mysterious, inexplicable force, or polarisation. As we have 
seen, the matter is not only no enigma, but on the contrary, a nec- 
essary psychological postulate. We should rather find the absence 
of this faculty incomprehensible. 

But everything I have just said presupposes a receptive brain. 
The formation of lasting perceptions and associations cannot take 
place without an organ capable of fixing the sense-impressions and 
of combining them among themselves. Experience shows that the 
immediate sensory centers are inadequate to the performance of 
this task. Though undoubtedly receptive, they are, nevertheless, 
incapable of utilising what has been received in the development 
of more complex instincts and can turn it to account only in the 
grosser, simpler reflexes and automatisms. To be sure, a male 
ant has better eyes than a worker ant, and probably quite as good 
antennae, but he is unable to remember what he has seen and is 
especially incapable of associating it in the form of a trail-image, 
because he is almost devoid of a brain. For this reason he is un- 
able to find his way back to the nest. On the other hand, it is well 
known that the brain of a man who has lost a limb or whose hear- 
ing is defective, will enable him to paint pictures with his foot, 
write with the stump of an arm or construct grand combinations 
from the images of defective senses. 

I venture, therefore, to designate as topochemical the olfactory 
antennal sense of honey-bees, humble-bees, wasps, etc. 


Can we generalise to such an extent as to apply this term with- 
out further investigation to all arthropods? To a considerable ex- 
tent this must be denied. 

In fact, the multiformity in the structure and development of 
the arthropod sense-organs is enormous, and we must exercise cau- 
tion in making premature generalisations. 

It is certain that in some aerial insects the olfactory sense has 
dwindled to a minimum, e. g., in those species in which the male 
recognises and follows the female exclusively by means of the eyes, 
as in the Odonata (dragon-flies). To insects with such habits an 
olfactory sense would be almost superfluous. Here, too, the an- 
tennae have dwindled to diminutive dimensions. 

But there are insects whose antennas are immovable and quite 
unable to touch objects. This is the case in most Diptera (flies). 
Still these antennae are often highly developed and present striking 
dilatations densely beset with olfactory papillae. By experiment I 
have demonstrated the existence of an olfactory sense in such 
Dipteran antennae, and I have been able to show that, e. g. , in 
Sarcophaga vivipara and other carrion flies, the egg-laying instinct 
is absolutely dependent on the sensation of the odor of carrion and 
the presence of the antennae. In these cases the contact-odor sense 
is undoubtedly absent. More or less of a topochemical odor-sense 
at long range must, of course, be present, since the antennae are 
external, but the precision of the spatial image must be very im- 
perfect, owing to the immobility of the antennae. Nevertheless, 
flies move about so rapidly in the air that they must be able by 
means of their antennae to distinguish very quickly the direction 
from which odors are being wafted. These insects do, in fact, find 
the concealed source of odors with great assurance. But this is no 
great art, for even we ourselves are able to do the same by sniffing 
or going to and fro. But the flies find their way through the air 
with their eyes and not at all by means of their sense of smell. 
Hence their olfactory powers probably constitute a closer psycho- 
logical approximation to those of mammals than to the topochemi- 
cal odor-sense of ants, for they can hardly furnish any constant and 
definite space-relations. 


Even in many insects with movable antennae and of less aerial 
habits, e. g., the chafers and bombycid moths, the antennal olfac- 
tory sense is evidently much better adapted to function at a dis- 
tance, i. e., to the perception of odors from distant objects, than 
to the perception of space and trails. Such insects find their way 
by means of their eyes, but fly in the direction whence their an- 
tennae perceive an odor that is being sought. 

A genuine topochemical antennal sense is, therefore, probably 
best developed in all arthropods, whose antennae are not only mov- 
able in the atmosphere, but adapted to feeling of objects. In these 
cases the still imperfect topochemical oder-sense for distances can 
be momentarily controlled by the contact-odor-sense and defini- 
tively fixed topographically, i. e., topochemically, as we see so ex- 
tensively practised in the ants. 

It would be possible to meet this view with the objection that 
a contact-odor sense could not accomplish much more than the 
tactile sense. I have made this objection to myself. But in the 
first place it is necessary to reckon with the facts. Now it is a fact 
that insects in touching objects with their antennae mainly perceive 
and distinguish the chemical constitution of the objects touched 
and heed these very much more than they do the mechanical im- 
pacts also perceived at the same time. Secondly, the tactile sense 
gives only resistance and through this, form. On the other hand, 
the multiplicity of odors is enormous, and it is possible to demon- 
strate, as I have done for the ants, and Von Buttel-Reepen for the 
bees, that these animals in distinguishing their different nest-mates 
and their enemies, betray nothing beyond the perception of ex- 
tremely delicate and numerous gradations in the qualities of odors. 

In combination with topochemical space-perception, these 
numerous odor-qualities must constitute a spatial sense which is 
vastly superior to the tactile sense. The whole biology of the so- 
cial Hymenoptera furnishes the objective proof of this assertion. 

It would certainly be well worth while to investigate this mat- 
ter in other groups of arthropods which possess complex instincts. 

In conclusion I will cite an example, which I have myself ob- 


served, for the purpose of illustrating the capacity of the topo- 
chemical olfactory sense. 

The American genus Eciton comprises predatory ants that 
build temporary nests from which they undertake expeditions for 
the purpose of preying on all kinds of insects. The Ecitons follow 
one another in files, like geese, and are very quick to detect new 
hunting grounds. As "ants of visitation," like the Africo-Indian 
species of Dorylus, they often take possession of human dwellings, 
ferret about in all the crevices of the walls and rooms for spiders, 
roaches, mice, and even rats, attack and tear to pieces all such 
vermin in the course of a few hours and then carry the booty home. 
They can convert a mouse into a clean skeleton. They also attack 
other ants and plunder their nests. 

Now all the workers of the African species of Dorylus and of 
many of the species of Eciton are totally blind, so that they must 
orient themselves exclusively by means of their antennal sense. 

In 1899 at Faisons, North Carolina, I was fortunate enough to 
find a temporary nest of the totally blind little Eciton carolinense in 
a rotten log. I placed the ants in a bag and made them the sub- 
ject of some observations. The Eciton workers carry their elon- 
gate larvae in their jaws and extending back between their legs in 
such a position that the antennas have full play in front. 

Their ability to follow one another and to find their way about 
rapidly and unanimously in new territory without a single ant go- 
ing astray, is incredible. I threw a handful of Ecitons with their 
young into a strange garden in Washington, i. e., after a long rail- 
way journey and far away from their nest. Without losing a mo- 
ment's time, the little animals began to form in files which were 
fully organised in five minutes. Tapping the ground continually 
with their antennae, they took up their larvae and moved away in 
order, reconnoitering the territory in all directions. Not a pebble, 
not a crevice, not a plant was left unnoticed or overlooked. The 
place best suited for concealing their young was very soon found, 
whereas most of our European ants under such conditions, i. e., in 
a completely unknown locality, would probably have consumed at 
least an hour in accomplishing the same result. The order and 


dispatch with which such a procession is formed in the midst of a 
totally strange locality is almost fabulous. I repeated the experi- 
ment in two localities, both times with the same result. The an- 
tennae of the Ecitons are highly developed, and it is obvious that 
their brain is instinctively adapted to such rapid orientation in 
strange places. 

In Colombia, to be sure, I had had opportunities of observing, 
not the temporary nests, but the predatory expeditions of larger 
Ecitons (E. Burchelli and hamatum} possessing eyes. But these 
in no respect surpassed the completely blind E. carolinense in their 
power of orientation and of keeping together in files. As soon as 
an ant perceives that she is not being followed, she turns back and 
follows the others. But the marvellous fact is the certainty of this 
recognition, the quickness and readiness with which the animals 
recognise their topochemical trail without hesitation. There is 
none of the groping about and wandering to and fro exhibited by 
most of our ants. Our species of Tapinoma and Polyergus alone 
exhibit a similar but less perfect condition. It is especially inter- 
esting, however, to watch the perpetuum mobile of the antennas of 
the Ecitons, the lively manner in which these are kept titillating 
the earth, all objects, and their companions. 

All this could never be accomplished by a tactile sense alone. 
Nor could it be brought about by an olfactory sense which furnished 
no spatial associations. As soon as an Eciton is deprived of its 
two antennas it is utterly lost, like any other ant under the same 
circumstances. It is absolutely unable to orient itself further or to 
recognise its companions. 

In combination with the powerful development of the cere- 
brum {corpora pedunculata) the topochemical olfactory sense of the 
antennae constitutes the key to ant psychology. Feeling obliged 
to treat of the latter in the preceeding lecture, I found it necessary 
here to discuss in detail this particular matter which is so often 

[In his latest Souvenirs entomologiques (Seventh Series) J. H. Fabre has 
recorded a number of ingenious experiments showing the ability of the males of 
Saturnia and Bombyx to find their females at great distances and in concealment. 


He tried in vain (which was to have been foreseen) to conceal the female by odors 
which are strong even to our olfactories. The males came notwithstanding. He 
established the following facts : (i) Even an adverse wind does not prevent the 
males from finding their way ; (2) if the box containing the female is loosely closed, 
the males come nevertheless ; (3) if it is hermetically closed (e. g., with wadding or 
soldered) they no longer come ; (4) the female must have settled for some time on 
a particular spot before the males come ; (5) if the female is then suddenly placed 
under a wire netting or a bell-jar, though still clearly visible, the males neverthe- 
less da. not fly to her, but pass on to the spot zuhere she had previously rested 
and left her odor ; (6) the experiment of cutting off the antennae proves very little. 
The males without antennas do not, of course, come again ; but even the other 
males usually come only once : their lives are too short and too soon exhausted. 

At first Fabre did not wish to believe in smell, but he was compelled finally, 
as a result of his own experiments, to eliminate sight and hearing. Now he makes 
a bold hypothesis : the olfactory sense of insects has two energies, one (ours), 
which reacts to dissolved chemical particles, and another which receives ' ' physical 
odor-waves," similar to the waves of light and sound. He already foresees how 
science will provide us with a " radiography of odors" (after the pattern of the 
Roentgen rays). But his own results, enumerated above under (4) and (5) contra- 
dict this view. The great distances from which the Bombyx males can discern 
their females is a proof to him that this cannot be due to dissolved chemical par- 
ticles. And these same animals smell the female only after a certain time and 
smell the spot where she had rested, instead of the female when she is taken away! 
This, however, would be inconceivable on the theory of a physical wave-sense, 
while it agrees very well with that of an extremely delicate, chemical olfactory 

It is a fact that insects very frequently fail to notice odors which we perceive 
as intense, and even while these are present, detect odors which are imperceptible 
to our olfactories. We must explain this as due to the fact that the olfactory pa- 
pillae of different species of animals are especially adapted to perceiving very differ- 
ent substances. All biological observations favor this view, and our psycho-chem- 
ical theories will have to make due allowance for the fact.] 


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